Surely if there was no successor, if the spiritual source has dried up, as it were, the Baha'i are like a shooting star?
Thus is the unique aspect of the Message given by Baha'u'llah Thomas. The Covernant was written by the Pen of the Messenger.
Imagine if Jesus himself had recorded that Peter was the Successor and that Upon Peter Jesus would build the Church, sealed that document and it was still available to this day. In turn what Peter offered after that, had the Authority of Christ, word for word. Imagine if this had been recorded by their pens and was still available to this day! There would be no possible cause of Division from that line. The records in the Gospels are there to confirm that, Jesus said that upon Peter's understanding that Jesus was the Christ, that the Church would be built. Yet we humans have a unique ways of making what is if God, try to fit into our own will and desires.
Islam had the same issue. Muhammad had appointed Ali verbally as His Successor, yet Ali was very young and on the death of Muhammad the older believers did not fulfil the request of Muhammad. The division of Sunnis and Shia happened immediately. That is another story, which is told in Revellation.
So Baha'u'llah had a written Covernant and appointed Abdul'baha and everything Abdul'baha gave us, is also of God. In turn Abdul'baha was given authority to appoint a successor, and Abdul'baha appointed Shoghi Effendi. All this is the continued line of Revelation from God.
Behind all this was the Authority for the appointment of the Hands of the Cause and for what is now known as the Universal House of Justice. This is a large topic, I will share a quote and a link to more from the Pen of Baha’u’llah.
"O ye Men of Justice! Be ye, in the realm of God, shepherds unto His sheep and guard them from the ravening wolves that have appeared in disguise, even as ye would guard your own sons. Thus exhorteth you the Counselor, the Faithful."
—
The Kitáb-i-Aqdas
That is from the book of Laws, more follow in the link.
https://www.bahai.org/the-universal-house-of-justice/articles-resources/from-writings-bahaullah
Shoghi Effendi had no one to appoint, but this was foreseen in the Writings of Baha'u'llah, a time when there might be no Guardian. This takes a great deal of study. So I will leave it at that.
So in summary, the Universal House of Justice has full authority to administer the Faith and guide it into the future. There can be no more authorised interpretation of scripture, we must move forward on what we have, allow for individual thoughts, but contain that process in an embracing unity, of all humanity.
All the best Thomas. Regards Tony